System and method for digital signal processing

ABSTRACT

A system and method for digital processing including a gain element to process an input audio signal, a high pass filter to then filter the signal and create a high pass signal, a first filter module to filter the high pass signal and create a first filtered signal and a splitter to split the high pass signal into two high pass signals. The first filter module filters one high pass signals before a first compressor modulates the signal or a high pass signal to create a modulated signal. A second filter module filters the modulated signal to create a second filtered signal that is processed by a first processing module including a band splitter that splits the signal into low and high band signals that are then modulated by compressors. A second processing module processes the modulated low and high band signals to create an output signal.

CLAIM OF PRIORITY

The present application is a continuation application of previouslyfiled, now pending application having Ser. No. 15/214,146, filed on Jul.19, 2016, which is set to mature into U.S. Pat. No. 9,906,858 on Feb.27, 2018, which is a continuation-in-part application of previouslyfiled Ser. No. 14/059,669, filed on Oct. 22, 2013, which matured intoU.S. Pat. No. 9,397,629 on Jul. 19, 2016, which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention provides for methods and systems for digitallyprocessing an audio signal. Specifically, some embodiments relate todigitally processing an audio signal in order to deliver studio-qualitysound in a variety of consumer electronic devices.

Description of the Related Art

Historically, studio-quality sound, which can best be described as thefull reproduction of the complete range of audio frequencies that areutilized during the studio recording process, has only been able to beachieved, appropriately, in audio recording studios. Studio-qualitysound is characterized by the level of clarity and brightness which isattained only when the upper-mid frequency ranges are effectivelymanipulated and reproduced. While the technical underpinnings ofstudio-quality sound can be fully appreciated only by experienced recordproducers, the average listener can easily hear the difference thatstudio-quality sound makes.

While various attempts have been made to reproduce studio-quality soundoutside of the recording studio, those attempts have come at tremendousexpense (usually resulting from advanced speaker design, costlyhardware, and increased power amplification) and have achieved onlymixed results. Thus, there exists a need for a process wherebystudio-quality sound can be reproduced outside of the studio withconsistent, high quality results at a low cost. There exists a furtherneed for audio devices embodying such a process in the form of computerchips embedded within audio devices, or within processing devicesseparate and standalone from the audio devices. There also exists a needfor the ability to produce studio-quality sound through inexpensivespeakers, as well as through a variety of readily available consumerdevices capable of reproducing sound, in both hardware-based andsoftware-based embodiments.

SUMMARY OF THE INVENTION

The present invention meets the existing needs described above byproviding for a system and method of digitally processing an audiosignal in a manner such that studio-quality sound can be reproducedacross the entire spectrum of audio devices. The present invention alsoprovides for the ability to enhance audio in real-time and tailors theenhancement to the audio signal of a given audio device or deliverysystem and playback environment.

The present invention may provide for a computer chip that can digitallyprocess an audio signal in such a manner, as well as provide for audiodevices that comprise such a chip or equivalent circuit combination. Thepresent invention may also provide for computer software readable andexecutable by a computer to digitally process an audio signal. In thesoftware embodiments, the present invention may utilize existinghardware and software components on computers such as PCs, Mac, andmobile devices, comprising various operating systems such as Android,iOS, and Windows.

Accordingly, in initially broad terms, an audio input signal is firstfiltered with a high pass filter. In at least one embodiment, the inputaudio signal is processed with a first gain element. In at least oneembodiment the first gain signal is then filtered with the high passfilter. The high pass filter, in at least one embodiment, is configuredto remove ultra-low frequency content from the input audio signalresulting in the generation of a high pass signal.

In at least one embodiment, the high pass signal from the high passfilter is then filtered through a first filter module to create a firstfiltered signal. The first filter module is configured to selectivelyboost and/or attenuate the gain of select frequency ranges in an audiosignal, such as the high pass signal.

In at least one embodiment, the first filter module boosts frequenciesabove a first frequency, and attenuates frequencies below a firstfrequency. In at least one embodiment, the high pass signal from thehigh pass filter is then split into a first high pass signal and asecond high pass signal.

In at least one embodiment, the first filtered signal from the firstfilter module is then modulated with a first compressor to create amodulated signal. In at least one embodiment, the second high passsignal is then filtered through a first filter module to create a firstfiltered signal. In at least one embodiment, the first high pass signalis then modulated with a first compressor to create a modulated signal.The first compressor is configured for the dynamic range compression ofa signal, such as the first filtered signal. Because the first filteredsignal boosted higher frequencies and attenuated lower frequencies, thefirst compressor may, in at least one embodiment, be configured totrigger and adjust the higher frequency material, while remainingrelatively insensitive to lower frequency material.

In at least one embodiment, the modulated signal from the firstcompressor is then filtered through a second filter module to create asecond filtered signal. The second filter module is configured toselectively boost and/or attenuate the gain of select frequency rangesin an audio signal, such as the modulated signal. In at least oneembodiment, the second filter module is configured to be in an at leastpartially inverse relation to the first filter module. For example, ifthe first filter module boosted content above a first frequency by +X dBand attenuated content below a first frequency by −Y dB, the secondfilter module may then attenuate the content above the first frequencyby −X dB, and boost the content below the first frequency by +Y dB. Inother words, the purpose of the second filter module in one embodimentmay be to “undo” the gain adjustment that was applied by the firstfilter module.

In at least one embodiment, the second filtered signal from the secondfilter module is then processed with a first processing module to createa processed signal. In at least one embodiment, the modulated signalfrom the first compressor is then processed with a first processingmodule to create a processed signal. In at least one embodiment, thefirst processing module may comprise a peak/dip module. In otherembodiments, the first processing module may comprise both a peak/dipmodule and a first gain element. The first gain element may beconfigured to adjust the gain of the signal, such as the second filteredsignal. The peak/dip module may be configured to shape the signal, suchas to increase or decrease overshoots or undershoots in the signal.

The processed signal from the first processing module is then split witha band splitter into at least low band signal and a high band signal. Inat least one embodiment, each band may comprise the output of a fourthorder section, which may be realized as the cascade of second orderbiquad filters.

The low band signal is modulated with a low band compressor to create amodulated low band signal, and the high band signal is modulated with ahigh band compressor to create a modulated high band signal. The lowband compressor and high band compressor are each configured todynamically adjust the gain of a signal. Each of the low band compressorand high band compressor may be computationally and/or configuredidentically as the first compressor.

At least the modulated low band signal and the modulated high bandsignal are then processed with a second processing module. The secondprocessing module may comprise a summing module configured to combinethe signals. The summing module in at least one embodiment mayindividually alter the gain of at least each of the modulated low band,and modulated high band signals. The second processing module mayfurther comprise a second gain element. The second gain element mayadjust the gain of the combined signal in order to create an outputsignal.

These and other objects, features and advantages of the presentinvention will become clearer when the drawings as well as the detaileddescription are taken into consideration.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature of the present invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIGS. 1A and 1B illustrate schematics of several embodiments of thepresent invention directed to systems for digitally processing an audiosignal.

FIGS. 2A, 2B, 2C, and 2D illustrate schematics of several otherembodiments of the present invention directed to systems for digitallyprocessing an audio signal.

FIGS. 3A, 3B, 3C, and 3D illustrate block diagrams of several otherembodiments of the present invention directed to methods for digitallyprocessing an audio signal.

FIG. 4A, 4B, 4C, and 4D illustrate block diagrams of several otherembodiment of the present invention directed to methods for digitallyprocessing an audio signal.

Like reference numerals refer to like parts throughout the several viewsof the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As illustrated by the accompanying drawings, the present invention isdirected to systems and methods for digitally processing an audiosignal. Specifically, some embodiments relate to digitally processing anaudio signal in order to deliver studio-quality sound in a variety ofdifferent consumer electronic devices.

As schematically represented, FIGS. 1A, 1B, 1C, and 1D illustrateseveral preferred embodiments of a system 100 for digitally processingan audio signal, and FIGS. 2A, 2B, 2C, and 2D provide examples ofseveral subcomponents and combinations of subcomponents of the modulesof FIGS. 1A, 1B, 1C, and 1D. Accordingly, and in at least one preferredembodiment, the systems 100 and 300 generally comprise an input device101, a high pass filter 111, a first filter module 301, a firstcompressor 114, a second filter module 302, a first processing module303, a band splitter 119, a low band compressor 130, a high bandcompressor 131, a second processing module 304, and an output device102. In at least another preferred embodiment, the systems 100 and 300generally comprise an input device 101, a high pass filter 111, asplitter 140, a first filter module 301, a first compressor 114, a firstprocessing module 303, a band splitter 119, a low band compressor 130, ahigh band compressor 131, a second processing module 304, and an outputdevice 102. In at least another embodiment, the systems 100 and 300 mayalso comprise a first gain element 103.

The input device 101 is at least partially structured or configured totransmit an input audio signal 201 into the system 100 of the presentinvention, and in at least one embodiment into the high pass filter 111.In at least another embodiment, the input device 101 is at leastpartially structured or configured to transmit an input audio signal 201into the system 100 of the present invention, into the first gainelement 103. The input audio signal 201 may comprise the full audiblerange, or portions of the audible range. The input audio signal 201 maycomprise a stereo audio signal. The input device 101 may comprise atleast portions of an audio device capable of audio playback. The inputdevice 101 for instance, may comprise a stereo system, a portable musicplayer, a mobile device, a computer, a sound or audio card, or any otherdevice or combination of electronic circuits suitable for audioplayback.

The high pass filter 111 is configured to pass through high frequenciesof an audio signal, such as the input signal 201, while attenuatinglower frequencies, based on a predetermined frequency. In other words,the frequencies above the predetermined frequency may be transmitted tothe first filter module 301 in accordance with the present invention. Inat least one embodiment, ultra-low frequency content is removed from theinput audio signal, where the predetermined frequency may be selectedfrom a range between 300 Hz and 3 kHz. The predetermined frequencyhowever, may vary depending on the source signal, and vary in otherembodiments to comprise any frequency selected from the full audiblerange of frequencies between 20 Hz to 20 kHz. The predeterminedfrequency may be tunable by a user, or alternatively be statically set.The high pass filter 111 may further comprise any circuits orcombinations thereof structured to pass through high frequencies above apredetermined frequency, and attenuate or filter out the lowerfrequencies.

The first filter module 301 is configured to selectively boost orattenuate the gain of select frequency ranges within an audio signal,such as the high pass signal 211. For example, and in at least oneembodiment, frequencies below a first frequency may be adjusted by ±XdB, while frequencies above a first frequency may be adjusted by ±Y dB.In other embodiments, a plurality of frequencies may be used toselectively adjust the gain of various frequency ranges within an audiosignal. In at least one embodiment, the first filter module 301 may beimplemented with a first low shelf filter 112 and a first high shelffilter 113, as illustrated in FIGS. 2A and 2B. In at least one otherembodiment, the first filter module 301 may be implemented only with afirst low shelf filter 112 as illustrated in FIG. 2D. In at least oneother embodiment, the first filter module 301 may be implemented onlywith a first high shelf filter 113 as illustrated in FIG. 2C. The firstlow shelf filter 112 and first high shelf filter 113 may both besecond-order filters. In at least one embodiment, the first low shelffilter 112 attenuates content below a first frequency, and the firsthigh shelf filter 113 boosts content above a first frequency. In otherembodiments, the frequency used for the first low shelf filter 112 andfirst high shelf filter 113 may comprise two different frequencies. Thefrequencies may be static or adjustable. Similarly, the gain adjustment(boost or attenuation) may be static or adjustable.

In at least one embodiment, the splitter 140 is configured to split asignal, such as the high pass signal 211 from the high pass filter 111.In at least one embodiment, the high pass signal 211 from the high passfilter 111 is split into a first high pass signal 210 and a second highpass signal 208.

The first compressor 114 is configured to modulate a signal, such as thefirst filtered signal 401 or the first high pass signal 210. The firstcompressor 114 may comprise an automatic gain controller. The firstcompressor 114 may comprise standard dynamic range compression controlssuch as threshold, ratio, attack and release. Threshold allows the firstcompressor 114 to reduce the level of the filtered signal 211 if itsamplitude exceeds a certain threshold. Ratio allows the first compressor114 to reduce the gain as determined by a ratio. Attack and releasedetermines how quickly the first compressor 114 acts. The attack phaseis the period when the first compressor 114 is decreasing gain to reachthe level that is determined by the threshold. The release phase is theperiod that the first compressor 114 is increasing gain to the leveldetermined by the ratio. The first compressor 114 may also feature softand hard knees to control the bend in the response curve of the outputor modulated signal 212, and other dynamic range compression controlsappropriate for the dynamic compression of an audio signal. The firstcompressor 114 may further comprise any device or combination ofcircuits that is structured and configured for dynamic rangecompression.

In at least one embodiment, the second filter module 302 is configuredto selectively boost or attenuate the gain of select frequency rangeswithin an audio signal, such as the modulated signal 214. In at leastone embodiment, the second filter module 302 is of the sameconfiguration as the first filter module 301. Specifically, the secondfilter module 302 may comprise a second low shelf filter 115 and asecond high shelf filter 116. In at least one embodiment, the secondfilter module 302 may comprise only a high shelf filer 116. The secondfilter module 302 may be configured in at least a partially inverseconfiguration to the first filter module 301. For instance, the secondfilter module may use the same frequency, for instance the firstfrequency, as the first filter module. Further, the second filter modulemay adjust the gain inversely to the gain or attenuation of the firstfilter module, of content above the first frequency. Similarly secondfilter module may also adjust the gain inversely to the gain orattenuation of the of the first filter module, of content below thefirst frequency. In other words, the purpose of the second filter modulein one embodiment may be to “undo” the gain adjustment that was appliedby the first filter module.

The first processing module 303 is configured to process a signal, suchas the second filtered signal 402, or the first modulated signal 214. Inat least one embodiment, the first processing module 303 may comprise apeak/dip module, such as 118 represented in FIGS. 2A, 2B, 2C, and 2D. Inother embodiments, the first processing module 303 may comprise a secondgain element 117. In various embodiments, the processing module 303 maycomprise both a second gain element 117 and a peak/dip module 118 forthe processing of a signal. The second gain element 117, in at least oneembodiment, may be configured to adjust the level of a signal by astatic amount. The second gain element 17 may comprise an amplifier or amultiplier circuit. In other embodiments, dynamic gain elements may beused. The peak/dip module 118 is configured to shape the desired outputspectrum, such as to increase or decrease overshoots or undershoots inthe signal. In some embodiments, the peak/dip module may further beconfigured to adjust the slope of a signal, for instance for a gradualscope that gives a smoother response, or alternatively provide for asteeper slope for more sudden sounds. In at least one embodiment, thepeak/dip module 118 comprises a bank of ten cascaded peak/dippingfilters. The bank of ten cascaded peaking/dipping filters may further besecond-order filters. In at least one embodiment, the peak/dip module118 may comprise an equalizer, such as parametric or graphic equalizers.

The band splitter 119 is configured to split a signal, such as theprocessed signal 403. In at least one embodiment, the signal is splitinto at least low band signal 220 and a high band signal 222, andpreferably also a mid band signal 221. Each band may be the output of afourth order section, which may be further realized as the cascade ofsecond order biquad filters. In other embodiments, the band splitter maycomprise any combination of circuits appropriate for splitting a signalinto three frequency bands. At least the low, and high bands, andpreferably a mid band may be predetermined ranges, or may be dynamicallydetermined based on the frequency itself, i.e. a signal may be splitinto three even frequency bands, or by percentage. The different bandsmay further be defined or configured by a user and/or control mechanism.

A low band compressor 130 is configured to modulate the low band signal220, and a high band compressor 131 is configured to modulate the highband signal 222. In at least one embodiment, each of the low bandcompressor 130 and high band compressor 131 may be the same as the firstcompressor 114. Accordingly, each of the low band compressor 130 andhigh band compressor 131 may each be configured to modulate a signal.Each of the compressors 130, 131 may comprise an automatic gaincontroller, or any combination of circuits appropriate for the dynamicrange compression of an audio signal.

A second processing module 304 is configured to process at least onesignal, such as the modulated low band signal 230 and the modulated highband signal 231, and preferably also a mid band signal 221. Accordingly,the second processing module 304 may comprise a summing module 132configured to combine a plurality of signals. The summing module 132 maycomprise a mixer structured to combine two or more signals into acomposite signal. The summing module 132 may comprise any circuits orcombination thereof structured or configured to combine two or moresignals. In at least one embodiment, the summing module 132 comprisesindividual gain controls for each of the incoming signals, such as themodulated low band signal 230 and the modulated high band signal 231,and preferably also a mid band signal 221. In at least one embodiment,the second processing module 304 may further comprise a third gainelement 133. The third gain element 133, in at least one embodiment, maybe the same as the second gain element 117. The third gain element 133may thus comprise an amplifier or multiplier circuit to adjust thesignal, such as the combined signal, by a predetermined amount. Theoutput device 102 may be structured to further process the output signal404. The output device 102 may also be structured and/or configured forplayback of the output signal 404.

As diagrammatically represented, FIGS. 3A, 3B, 3C, 3D, 4A, 4B, 4C, and4D illustrate other embodiments directed to a method for digitallyprocessing an audio signal, which may in at least one embodimentincorporate the components or combinations thereof from the systems 100and/or 300 referenced above. Each step of the method in FIGS. 3A, 3B,3C, 3D, 4A, 4B, 4C, and 4D as detailed below may also be in the form ofa code segment directed to at least one embodiment of the presentinvention, which is stored on a non-transitory computer readable medium,for execution by a computer to process an input audio signal.

Accordingly, an input audio signal is filtered, as in 501, with a highpass filter to create a high pass signal. Alternatively, the input audiosignal is first processed, as in 510, with a first gain element tocreate a first gain signal. The high pass filter is configured to passthrough high frequencies of a signal, such as the input signal, or thefirst gain signal, while attenuating lower frequencies. In at least oneembodiment, ultra-low frequency content is removed by the high-passfilter. In at least one embodiment, the high pass filter may comprise afourth-order filter realized as the cascade of two second-order biquadsections. The reason for using a fourth order filter broken into twosecond order sections is that it allows the filter to retain numericalprecision in the presence of finite word length effects, which canhappen in both fixed and floating point implementations. An exampleimplementation of such an embodiment may assume a form similar to thefollowing:

-   -   Two memory locations are allocated, designated as d(k-1) and        d(k-2), with each holding a quantity known as a state variable.        For each input sample x(k), a quantity d(k) is calculated using        the coefficients a1 and a2:

d(k)=x(k)−a1*d(k-1)−a2*d(k-2)

-   -   The output y(k) is then computed, based on coefficients b0, b1,        and b2, according to:

y(k)=b0*d(k)+b1*d(k-1)+b2*d(k-2)

The above computation comprising five multiplies and four adds isappropriate for a single channel of second-order biquad section.Accordingly, because the fourth-order high pass filter is realized as acascade of two second-order biquad sections, a single channel of fourthorder input high pass filter would require ten multiples, four memorylocations, and eight adds.

The high pass signal from the high pass filter is then filtered, as in502, with a first filter module to create a first filtered signal. Thefirst filter module is configured to selectively boost or attenuate thegain of select frequency ranges within an audio signal, such as the highpass signal. Accordingly, the first filter module may comprise a secondorder low shelf filter and a second order high shelf filter in at leastone embodiment. In at least one embodiment, the first filter moduleboosts the content above a first frequency by a certain amount, andattenuates the content below a first frequency by a certain amount,before presenting the signal to a compressor or dynamic rangecontroller. This allows the dynamic range controller to trigger andadjust higher frequency material, whereas it is relatively insensitiveto lower frequency material.

In at least one embodiment, the high pass signal 211 from the high passfilter 111 is split, as in 511, with a splitter 140, into a first highpass signal 210, and a second high pass signal 208. In at least oneembodiment, the second high pass signal is filtered with a first filtermodule. In at least one embodiment the first filtered signal 401 fromthe first filter module 301 is then modulated, as in 503, with a firstcompressor 114. In at least one embodiment, the first high pass signal210 is modulated with a first compressor 114 as in 513. The firstcompressor may comprise an automatic or dynamic gain controller, or anycircuits appropriate for the dynamic compression of an audio signal.Accordingly, the compressor may comprise standard dynamic rangecompression controls such as threshold, ratio, attack and release. Anexample implementation of the first compressor may assume a form similarto the following:

-   -   The compressor first computes an approximation of the signal        level, where att represents attack time; rel represents release        time; and invThr represents a precomputed threshold:        -   temp=abs(x(k))        -   if temp>level (k-1)

level(k)=att * (level(k-1)-temp)+temp else

level=rel (level(k-1)-temp)+temp

-   -   This level computation is done for each input sample. The ratio        of the signal's level to invThr then determines the next step.        If the ratio is less than one, the signal is passed through        unaltered. If the ratio exceeds one, a table in the memory may        provide a constant that's a function of both invThr and level:        -   if (level * thr<1)            -   output(k)=x(k)        -   else            -   index=floor(level* invThr)        -   if (index>99)            -   index=99        -   gainReduction=table[index]        -   output(k)=gainReduction x(k)

In at least one embodiment, the modulated signal from the firstcompressor is then filtered, as in 504, with a second filter module tocreate a second filtered signal. The second filter module is configuredto selectively boost or attenuate the gain of select frequency rangeswithin an audio signal, such as the modulated signal. Accordingly, thesecond filter module may comprise a second order low shelf filter and asecond order high shelf filter in at least one embodiment. In at leastone embodiment, the second filter module boosts the content above asecond frequency by a certain amount, and attenuates the content below asecond frequency by a certain amount. In at least one embodiment, thesecond filter module adjusts the content below the first specifiedfrequency by a fixed amount, inverse to the amount that was removed bythe first filter module. By way of example, if the first filter moduleboosted content above a first frequency by +X dB and attenuated contentbelow a first frequency by −Y dB, the second filter module may thenattenuate the content above the first frequency by −X dB, and boost thecontent below the first frequency by +Y dB. In other words, the purposeof the second filter module in one embodiment may be to “undo” thefiltering that was applied by the first filter module.

In at least one embodiment, the second filtered signal from the secondfilter module is then processed, as in 505, with a first processingmodule to create a processed signal. In at least one embodiment, themodulated signal from the first compressor is then processed, as in505′, with a first processing module to create a processed signal. Theprocessing module may comprise a second gain element configured toadjust the level of the signal. This adjustment, for instance, may benecessary because the peak-to-average ratio was modified by the firstcompressor. The processing module may comprise a peak/dip module. Thepeak/dip module may comprise ten cascaded second-order filters in atleast one embodiment. The peak/dip module may be used to shape thedesired output spectrum of the signal. In at least one embodiment, thefirst processing module comprises only the peak/dip module. In otherembodiments, the first processing module comprises a gain elementfollowed by a peak/dip module.

The processed signal from the first processing module is then split, asin 506, with a band splitter into at least a low band signal and a highband signal, and preferably also a mid band signal. The band splittermay comprise any circuit or combination of circuits appropriate forsplitting a signal into a plurality of signals of different frequencyranges. In at least one embodiment, the band splitter comprises afourth-order band-splitting bank. In this embodiment, each of the lowband and high band, and preferably also a mid band, are yielded as theoutput of a fourth-order section, realized as the cascade ofsecond-order biquad filters.

The low band signal is modulated, as in 507, with a low band compressorto create a modulated low band signal. The low band compressor may beconfigured and/or computationally identical to the first compressor inat least one embodiment. The high band signal is modulated, as in 508,with a high band compressor to create a modulated high band signal. Thehigh band compressor may be configured and/or computationally identicalto the first compressor in at least one embodiment.

At least the modulated low band signal and modulated high band signal,and preferably also a mid band signal, are then processed, as in 509,with a second processing module. The second processing module comprisesat least a summing module. The summing module is configured to combine aplurality of signals into one composite signal. In at least oneembodiment, the summing module may further comprise individual gaincontrols for each of the incoming signals, such as the modulated lowband signal and the modulated high band signal, and preferably also amid band signal. By way of example, an output of the summing module maybe calculated by:

out=w0*low+w1*mid+w2*high

The coefficients w0, w1, and w2 represent different gain adjustments.The second processing module may further comprise a second gain element.The second gain element may be the same as the first gain element in atleast one embodiment. The second gain element may provide a final gainadjustment. Finally, the second processed signal is transmitted as theoutput signal.

As diagrammatically represented, FIG. 4 illustrates another embodimentdirected to a method for digitally processing an audio signal, which mayin at least one embodiment incorporate the components or combinationsthereof from the systems 100 and/or 300 referenced above. Because theindividual components of FIG. 4 have been discussed in detail above,they will not be discussed here. Further, each step of the method inFIG. 4 as detailed below may also be in the form of a code segmentdirected to at least one embodiment of the present invention, which isstored on a non-transitory computer readable medium, for execution by acomputer to process an input audio signal.

Accordingly, an input audio signal such as the first gain signal isfirst filtered, as in 501, with a high pass filter. The high pass signalfrom the high pass filter is then filtered, as in 601, with a first lowshelf filter. The signal from the first low shelf filter is thenfiltered with a first high shelf filter, as in 602. The first filteredsignal from the first low shelf filter is then modulated with a firstcompressor, as in 503. In at least one embodiment, the modulated signalfrom the first compressor is filtered with a second low shelf filter asin 611. The signal from the low shelf filter is then filtered with asecond high shelf filter, as in 612. In at least one embodiment, themodulated signal from the first compressor is filtered with a secondhigh shelf filter as in 612′. In at least one embodiment, the secondfiltered signal from the second low shelf filter, is then gain-adjustedwith a second gain element, as in 621. In at least one embodiment, thesecond filtered signal from the second high shelf filter, is thengain-adjusted with a second gain element, as in 621. The signal from thesecond gain element is further processed with a peak/dip module, as in622. The processed signal from the peak/dip module is then split into atleast a low band signal and a high band signal, but preferably also amid band signal, as in 506. The low band signal is modulated with a lowband compressor, as in 507. The high band signal is modulated with ahigh band compressor, as in 508. At least the modulated low band signaland modulated high band signal, and also preferably a mid band signal,are then combined with a summing module, as in 631. The combined signalis then gain adjusted with a third gain element in order to create theoutput signal, as in 632.

Any of the above methods may be completed in sequential order in atleast one embodiment, though they may be completed in any other order.In at least one embodiment, the above methods may be exclusivelyperformed, but in other embodiments, one or more steps of the methods asdescribed may be skipped

Since many modifications, variations and changes in detail can be madeto the described preferred embodiment of the invention, it is intendedthat all matters in the foregoing description and shown in theaccompanying drawings be interpreted as illustrative and not in alimiting sense. Thus, the scope of the invention should be determined bythe appended claims and their legal equivalents. Furthermore, in thatvarious embodiments may include one, two or three of a specific element,such as a gain controller, reference to them as first, second and thirdis included for facilitated reference when more than one is included,but should not be viewed as limiting to require one, two or three in anyor all instances. For example, reference to a second gain element doesnot require that all embodiments include a first gain element.

Now that the invention has been described,

What is claimed is:
 1. A system for digital signal processing of aninput audio signal comprising: a high pass filter configured to filteran audio signal to create a high pass signal, a first filter moduleconfigured to filter the high pass signal to create a first filteredsignal, a first compressor configured to modulate the first filteredsignal to create a modulated signal, a second filter module configuredto filter the modulated signal to create a second filtered signal, afirst processing module configured to process the second filtered signalto create a processed signal, a band splitter configured to split theprocessed signal into at least a first low band signal and a second highband signal, at least one modulator structured to modulate said firstband signal and said second band signal to create a first and a secondmodulated band signal, and a second processing module configured toprocess at least said first and said second modulated band signals tocreate an output signal.
 2. A system as recited in claim 1 wherein thefirst filter module comprises: a first low shelf filter configured tofilter the high pass signal to create a first low shelf signal, a firsthigh shelf filter configured to filter the first low shelf signal tocreate the first filtered signal.
 3. A system as recited in claim 1wherein said second filter module comprises: a second low shelf filterconfigured to filter the modulated signal to create a second low shelfsignal, and a second high shelf filter configured to filter second lowshelf signal to create the second filtered signal.
 4. A system asrecited in claim 1 wherein said first filter module comprises a lowshelf filter and said second filter module comprises a high shelffilter.
 5. A system as recited in claim 1 further comprising a firstgain element configured to adjust a gain of the input audio signal priorto said high pass filter.
 6. A system as recited in claim 1 wherein saidfirst processing module comprises a gain element configured to adjustthe gain of the second filtered signal to create a gain signal; and apeak/dip module configured to process the gain signal to create theprocessed signal.
 7. A system as recited in claim 1 wherein said secondprocessing module comprises: a summing module configured to combine atleast the first and second modulated band signals to create a combinedsignal, and a gain element configured to adjust the gain of the combinedsignal to create the output signal.
 8. A system as recited in claim 1wherein said band splitter splits the processed signal into at least alow band signal and a high band signal, and said at least one modulatorcomprises a band compressor.
 9. A system as recited in claim 8 whereinsaid at least one modulator comprises a low band modulator and a highband modulator.